Wave-signal translating channel



Aug. 17, 1943. N. P. cAsE WAVE-SIGNAL TRANSLATING CHANNEL Filed May 8, 1942 INVENTOR NE LSO N P. CASE BY W ATTORNEY fa Patented Aug. 17, 1943 WAVE-SIGNAL TRANSLATING CHANNEL Nelson P. Case, Great Neck, N. Y., assignor to Hazeltine Corporation, a corporation of Delav ware Application May 8, 1942, Serial No. 442,158

Claims. (01. 178-44) The present invention relates to wave-signal translating channels and, particularly, to such channels of thetype adapted to translate wave signal selectively in either direction through the channel. While the invention is of general application, it is particularly suited for use in coupling an antenna-ground system to a wave-signal apparatus adapted both to transmit and receive wave signals. 4

In many instances, it is desirable to translate wave signals selectively in either direction through a wave-signal translating channel. For example, a

a rather simple form of portable wave-signal apparatus for two-way communication utilizes an oscillator in common to both transmitting and receiving apparatus. 1 This oscillator is coupled to an antenna-ground system and is used in conven disadvantage of the superregenerative type of detector, it is customary to isolate the detector from the antenna-ground system by the use of a buffer amplifier stage which couples the antenna system to the detector. However, in the two-way communication apparatus previously referred to, it

' was pointed out that the oscillator is used not only as a superregener'ative detector but also as an oscillator for generating wave signals for purposes of transmission. In such case, one can no longer use a simple buffer amplifier stage for the purpose described but must use a two-way wavesignal translating channel by which wave signals may be translated through the channelin one di-. rection during transmission and in the opposite direction during'reception.

In an arrangement of the type just described, a two-way wave-signal translating channel might simply comprise two amplifier stages coupled in parallel but in opposite senses between the antenna system and the wave-signal communication apparatus and adapted, upon selective energization of the amplifiers, to translate wave signals in opposite directions. Such an arrangement,

however, is not a complete solution to the prob- -lem since the amplifier vacuum tubes have in- I ternal capacitances which tend to cause undesired translation of wave-signal energy in a direction opposite to the desired direction. It would be desirable, therefore, to provide in an arrangement of the type described, a two-way wavesignal translating channel of simple circuit arrangement involving a minimum of circuit components and yet one which possesses a high degree of freedom from undesired translation of wave signals in a direction opposite to a desired direction. I

Itis an object of the present invention, therefore, to provide anew and improved wave-signal translating channel adapted to translate Wave signals selectively in either direction through the channel.

It is a further object of the invention to provide a new and improved wave-signal translating channel of the type described and one having substantially complete freedom from undesired translation of wave signals through the channel in a direction opposite to a selected direction.

It is an additional object of the invention to provide a wave-signal translating channel of the type described wherein certain of th circuit components perform their usual functions when wave signals are translated in one direction through the channel but perform other and totally unrelated functions when the translation ofwave signals through the channel occurs in the opposite,

direction, thus providing a wave-signal translating-channel of simplified and improved circuit arrangement involving a minimum of circuit components.

In accordance with the invention, a wave-signal translating channel comprises. a pair of terminal circuits for the channel, a pair of-vacuumtube repeater devices, and means for coupling the devices between the terminal circuits to effect translation of wave signals between the terminal circuits in one direction through one of the devices and in an opposite direction through the other of the devices. :Each of the devices and its associated coupling means have undesirable reactance tending to produce undesirable translation of wave signals between the terminal circuits in a direction opposite to its direction of normal translation. 'I'htranslating channel includes means for selectively energizing the repeater devices to effect translation of wave signals in a selected direction between the terminal circuits, and means for reducing the tendency of 5 a selected device undesirably to translate wave antenna-ground system signals in the direction opposite to the selected direction comprising means including the undesirable reactance of the nonselected one of the devices and its associated coupling means for neutralizing the undesirable reactance of the selected device and its associated coupling means.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the fOlloWing description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring now to the drawing,the single figure thereof is a circuit diagram, partly schematic, of a complete two-way communication wavesignal apparatus embodying the present invention in a preferred form.

Referring now more particularly to the drawing, the wave-signal apparatus in general includes an antenna-ground system III, II having an adjustable condenser l2 and an inductor 3 included in series therein for tuning the antennaground system to a predetermined operating frequency. The antenna-ground system is connected to a terminal circuit comprising terminals |4, |5 of a wave-signal translating channel l6, more fully described hereinafter. The translating channel I 6 includes a second terminal circuit comprising terminals II, 8 which are connected to terminals 9, of a two-way wavesignal communication apparatus 2|. The latter in its simplest form includes an oscillator which is used to generate a wave signal for transmission and is also used as a superregenerative detector to derive the modulation components of a received wave signal. The two functions of the oscillator are controlled by a manuallyadjustable transmit-receive switch 22. In the transmit position T of switch 22; a microphone 23 is coupled through suitable amplifiers and a modulator stage to the oscillator of unit 2| to modulate the wave signal generated thereby in just described may, with the exception of the signal-translating channel l6, be of a conventional construction and operation, the details of which are well known in the art, rende ing detailed description thereof unnecessary. Considering briefly the operation of the wave-signal apparatus as a whole, and neglecting for the moment the operation of the signal-translating channel l6 presently to be described, upon operation of the switch 22 to thetransmit position T, wave signals are generated by the oscillator of unit 2| and, after modulation by a speech signal derived from the microphone 23, are translated through the signal-translating channel "5 to the Ill, II for radiation thereby. Upon operation of the switch 22 to the receive position R, wave signals received by the antenna-ground system III, II are translated through the wave-signal translating channel |6 to the apparatus 2| .where the oscillator of this C unit, now operating as a superregenerative detector, derives the modulatlonicomponents of the received wave signal. The modulation components are amplified by the amplifier stages of unit 2| and are applied to the sound reproducer 24 for reproduction in a conventional manner.

Referring now more particularly to the portion of the system embodying the present invention, the wave-signal translating channel l6 comprises a pair of terminal circuits 25, 26. The terminal circut 25 includes a winding 21 connected to the terminals |4, l5 and a winding 28 inductively coupled to the winding 21 and tunable by a condenser 29 to the frequency of the wave signals to be translated by the channel IS. The terminal circuit 26 similarly includes a winding 30, connected to the terminals l8 and tunable'by a condenser 3| to the selected operating frequency or frequency of the wave signals to be translated by the channel l6, and a winding 32 inductively coupled to the winding 30 and tapped at a point P to provide a winding section 3211. on one side of tap P and a Winding section 32b on the other side of said tap. The translating channel also includes a pair of vacuum-tube repeater devices 33, 34 each including input and output electrodes. Specifically, the repeater device 33 includes input electrodes comprising a control electrode 35 and a cathode or filament 36, the latter being energized from an energizing source indicated as +A through a cathode circuit including a first contact R of a switch 31. This repeater device also includes output electrodes comprising an anode 38 and the cathode 36. The correspondingelectrodes of the repeater device 34 are indicated by the same reference numerals primed, the cathode 36 of this device being connected to a second 1 switch contact T of the switch 31 to be selectively energized from the source +A. The switch 31 thus comprises means for selectively energizing the repeater devices 33, 34, specifically for energizing the cathode circuits of the repeater devices, to effect translation of wave signals in a selected direction between the terminal circuits 25 and 26.

The translating channel l6 includes means for coupling the vacuum-tube repeater devices 33, 34 between the terminal circuits 25 and 26 to efiect translation of wave signals between the terminal circuits in one direction through one of the devices and in an opposite direction through the other of the devices. This means comprises a condenser 39 and grid resistor 45 for coupling the input electrodes 35, 36 of the repeater device 33 to the terminal circuit 25, and a similar condenser 40 and grid resistor 46, together with a condenser 44, for coupling the input electrodes 35', 36' of the repeater device 34 to the terminal circuit 26 and particularly to the section 32a of the winding 32 lying above the tap P. The last-named means also includes a connection of the anode 38 of. vacuum tube 33 through the section 32b of the winding 32 of terminal circuit 26 to a source of space current indicated as +3, and includes a similar connection of the anode 38 of the repeater device 34 through the winding 28 of the terminal circuit 25 to a source of space current indicated as +13 The switch 31 preferably is connected for unicontrol operationwith the witch 22 of unit 2| as indicated by the broken line 4|.

In considering the operation of the wavesignal translating channel just described, assume that it is desired to receive wave signals and to translate such received wave signals from the antenna-ground system H], II through the translating channel 5 to the receiving apparatus of unit 2|. In this case, the switch 22 of unit 2| is moved to the receive position R, thus simultaneand selectively energizing the cathode circuit of the vacuum-tube repeater device 33. The latter thereupon operates in conventional manner as-a repeater device to translate wavesignals, applied from the antenna-ground system In, H and the terminal circuit to the terminal circuit 26 and thus to the circuit terminals I9, 20 of the unit 2|, the control electrode developing across the resistor 45 a self-bias potential by peak rectification of the applied wave signals.

However, the oscillator of unit 2| is used during reception as a superregenerative detector and the oscillations generated thereby are applied to the'terminal circuit 26 and hence through the section 32b of winding 32 to the anode 38 of the repeater device 33. Now it is well known that there is a certain amount of undesirable capacitive reactance caused by the inherent interelectrode capacitance between the anode 38 and the control electrode 35 of the repeater device 33 and signal which might cause interference with other nearby receivers operating on the same frequency. Now assume that it is desired to transmit a wave signal generated by the oscillator of unit also certain inherent and undesired capacitive reactance caused by the capacitance between the anode or output circuit and the control-electrode or inputcircuit comprising the coupling means of this device. Such undesired capacitance is represented by the dotted-line condenser 42. Thus, when the oscillations generated by the oscillator of unit 2 I, while such oscillator is operating as a superregenerative detector, are applied to the anode 38. of the repeater device 33, the

.undesirable capacitance 42 tends to produce undesired translation of wave signals from the terminal circuit 26 to the terminal circuit 25 which is in a direction opposite to the direction of normal translation of the repeater device 33.

It is for the purpose of redhcing the tendency i of a selected repeater device undesirable to translate wave signals in a' direction opposite to its direction of normal translation that the tapped winding 32 of the terminal circuit 26 is used and the repeater devices 33 and 34 are coupled to this tapped winding in the manner previously described. Thus, the oscillations generated by the oscillator of unit 2!, while such oscillator operates, as a superregenerative detector, are not only applied to the anode 38 of the device 33 through the section 32b of the'winding 32, but are also applied through the section 32a of this winding and condenser 40 to the control electrode 35' of the repeater device 34; The latter device also has capacitive reactance caused by the inherent capacitance between its anode 38' and its control electrode 35', commonly referred to as interelectrode capacitance, and capacitive reactance caused by capacitancebetween its associated coupling means comprising its input and output circuits, such capacitance being represented by the dotted-line condenser 43. Now if the capacitances 42 and 43 are equal, as is generally the case since'the repeater devices 33 and 34 are similar and involve similar circuit arrangements, the tap P is made at the center point of the winding 32. In this event, the oscillations which are applied throuvh the capacitance 42 to the terminal circuit 25 from the anode 38 of device 33, under the operating condition assumed, are neutralized by oscillations of equal amplitude but opposite phase applied to the terminal circuit 25 through the capacitance 43 from the'control electrode 35' of repeater device 34. These two oscillatory voltages, being of equal amplitude and opposite phase at the input circuit 25, completely neutralize each other and hence no oscillatory voltage. is applied to the antenna system [0, H for radiation thereby as an undesirable wave 2|. In that case, the switch 22 is moved to its transmit position T, thereby moving the switch 31 of the translating channel l6 to close its terminal 'T, thus energizing the cathode circuit of the repeater device 34 and deenergizing that of the repeater device 33. Th repeater device 34 of the channel l6'thereupon operates in conventional manner to translate or repeat wave signals applied to the terminal circuit 26 from the oscillator of unit 2|, the translated oscillations being applied through the terminal circuit 25 to the antenna system "I, l I for radiation thereby, the control electrode 35' developing a self-bias potential across the resistor 46 by peak rectification of the applied wave-signals. Due to the capacitance 43 of therepeater device 34 and its associated coupling means, a portion of the energy translated to the terminal circuit 25 is fed back to the input circuit of the device 34. Unless the effect of such feed-back energy is neutralized, the, repeater device 34 tends to break into sustained oscillation. This is undesirable not only from the standpoint that such oscillations are radiated by the antenna 10, I I as an undesired spurious wave signal, but also for the resistance of tube 33.

reason that the repeater device 34 no longer is capable of translating with fidelity the modulated wav signal. The tendency of the repeater device 34 undesirably to translate such feed-back energy in the direction opposite to the normal direction of translation of energy through this device is reduced by the capacitance 42 of the nonselected repeater device 33 nd its a s ciated coupling means. Thus, feed-back energy from ,the terminal circuit 2515 applied by virtue of the capacitance 43 to the section 320, of winding 32 and feed-back energy of the same magnitude and phase is also applied through the capacitance 42 to the section 3212 of winding 32. Now since the magnitude of the amounts of feed-back energy appliedto the terminal circuit 26 through the capacitances 42 and 43 are equal and since they are applied with the same phase to oppositesections 32a and 32b of the winding 32, no feed-back energy is applied to the input circuit of the repeater device 34 with the result that there is no tendency of this device to break into sustained oscillation.

'Upon selection of the repeater device 34 to translate wave signals from the terminal circuit 26 to the terminal circuit 25, the effective resistance of the tuned circuit 30, 3| is determined in large part by the values of resistance of the input circuit of tube 34 or, in other words, by the value of resistance of the resistor 46 and the resistance between the control electrode 35' and the cathode 36 of tube 34 when the con rol electrode 35' conducts current. On the other hand, when the repeater device 33 is selectively energized to translate wave signals from the terminal circuit 25 to the terminal circuit 26, the efiective resistance of the tuned circuit 30, 3| is determined in large part by the values of resistance of both the input circuit of tube 34 and the output circuit of tube 33. The resistance of the input circuit of tube 34 under this condition comprises only the value of resistance of the resistor 46, 'since the control electrode 35 no longer conducts current, whereas the resistance of the output circuit of tube 33 comprises the anode-cathode 'Now it is known that the resonant frequency of a circuit containing inductance L, capacitance C and resistance R is determined by the relation:

1 R 170 7 Ordinarily, th value of resistance R in a tuned circuit is not only constant but is small in comparison with the reactive impedance of the tunedcircuit inductor and, as shown by Equation 1, does not play an important part in determining the frequency of the circuit. Where the tuned circuit determines the frequency of generated oscillations, as is the 'case of the tuned, circuit 30, 3| which is the frequency-determining circuit of th oscillator of unit 2|, changes of resistance of the tuned circuit may materially affect the frequency of the generated oscillations. In the present arrangement, any change of frequency of the tuned circuit.30, 3|, due to selective energization of the repeater devices 33 and 34, is undesirable since such equipments normally are used at least in pairs and, in the event that each unit does not transmit and receive on the same 1 operating frequency, attempts to keep the two units in tune with each other during repeated two-way communications are very likely to result in progressive shift of the operating frequency from an assigned value.

In order, therefore, that the resonant frequency of the tuned circuit 30, 3| shall not vary with selective energization of the devices 33 and 34, it is essential that the efiective values of resistance which are coupled into the tuned circuit 30, 3| from the output circuit of the repeater device 33 and the input circuit of the repeater device 34 should be the same regardless of the selective energization of the repeater devices. Now when the repeater device 34 is selectively energized, as by movement of the switch 31 to close its contact T, the resistance coupled into the tuned circuit 30, 3| comprises only the input-circuit resistance of the repeater device 34 which has the value:

where: I R46=the value of resistance of the resistor 46,

R;c=the effective resistance between the control electrode 35' and cathode 36' of tube 34 when the control electrode conducts current.

to the ohmic resistance of the space current path.

Hence, the input-circuit resistance of tube 34, under this condition of operation, has the value:

R1 R45 T (3) The Value of the resistance coupled into the tuned circuit 30, 3| when the repeater device 33 is selectively energized is given by the relation:

R =the anode-cathode or output resistance of repeater device 33 in its conductive state.

Now if the effective value of resistance R1 be determined from devices 33 and 34.

coupled into the tuned circuit 30, 3| when the repeater device 34 is energized is equal to the eilective value of resistance R2 which is coupled 30, 3| when the repeater into the tuned circuit, device 33 is energized, the resonant frequency of the tuned circuit 30, 3| is not changed by the selective energization of the repeater devices 33, 34. This is most readily accomplished by proportioning the value of the resistor 46 with relation to the anode-cathode resistance of the repeater device 33. The value of the resistor 46 which satisfies the required conditions is found from the solution of Equations 3 and 4 and is:

In this manner the impedance values of the input circuit parameters of repeater device 34 are so proportioned with relationto the impedance values of the output circuit of the parameters of the other repeater device 33 in its conductive state that the resonantfrequency of the tuned circuit 30, 3| is substantially constant with selective energization of the devices 33 and 34.

In the event that the repeater devices 33 and 34 are not similar, whereby the values of the capacitances 42 and '43 are not equal, th point at which the tap P is made on the win mg 32 of "the terminal circuit 26, is adjusted accordingly to insure that any wave-signal voltage translated from one terminal circuit to the other through the inherent capacitance of a selected device has a magnitude at such other terminal circuit *equal to the same wave-signal voltage translated through the nonselected device. Thus, if the capacitance 43 is larger than the capacitance 42, the tap P will be made on the winding 32 at such point that the section 32a is proportionally smaller than the section 32b. vShould the tap P be changed to a point on the winding 32 other than the central point thereof, the value of resistor '46 likewise must be modified to insure that the eifective resistance which is coupled into the tuned circuit 30, 3| shall be constant regardless of the selective energization of the repeater The new value which the resistor 46 should have in this event may readily the principles given above.

From the above description of the invention, it willbe evident that the wave-signal translating channel I 6 includes means for reducing the tendrepeater device undesirably to translate wave signals in the direction opposite direction comprising means including the undesirable reactance of the nonselected one of the devices and its associated coupling means for neutralizing the undesirable reactance of the selected device and its associated coupling means. The last-named means includes the tapped winding 32 of the terminal circuit 26, this tappedtwinding being effective to opposite direction by the selected repeater device. Consequently,'the neutralizing means includes the other section of the tapped winding.

While in the arrangement described the means for selectively energizing the repeater devices 33 and 34 comprises the switch 31, it will be evident that other means of selective energization may be employed. For example, selective values of bias may be applied to the control electrodes 35 and 35' of the respectiverepeater devices 33 and 34 by which to control these devices in the manner and for the purpose described.

There occurs a Very slight change in the interelectrode capacitance of the repeater devices 33 and 34 when the energization of these devices is changed. In the event that such change of capacitance in a particular application prevents exact neutralization for both directions of trans? lation of wave signals for a given point at which the tap P is made on the winding 32, exact neutralization may nevertheless be efiected either by making the tap P adjustable on the winding 32 and by mechanically connecting the tap for unicontrol operation with the switches 22 and 31, or by letting the tap P remain fixed and by using me or more. condensers of small capacitance which are selectively connected in shunt to one or both of the capacitances 42 and 43 by a suitable switch operated in unicontrol with the switch While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modiflcations may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A wave-signal translating channel comprising, a pair of terminal circuits forsaid channel, a pair of vacuum-tube repeater devices, means for coupling said devices between said terminal circuits to effect translation of wave signals bethrough one of said devices and in an opposite direction through the other of said devices, each of said devices having inherent interelectrode capacitance tending to produce undesirable translation of wave signals between said terminal circuits in a direction opposite to its direction of normal translation, means for selectively ener gizing said repeater devices to effect translation of wave signals in a selected direction between said terminal circuits, and means for reducing the tendency of a selected device undesirably to tween said terminal circuits in one direction through one of said devices and in an opposite direction through the other of said devices, each of said devices and its associated coupling means having undesirable reactance tending to produce undesirable translation of wave signals between said terminal circuits in a direction opposite to its direction of normal translation,means for selectively energizing said repeater devices to effect translation of wave signals in a selected direction between said terminal circuits, and means for reducing the tendency of a selected device undesirably to translate wave signals in the direction opposite to said selected direction comprising means including the undesirable reactance of the nonselected one of said devices and its associated coupling means for neutralizing the undesirable reactance of said selected device and its associated coupling means.

2. A wave-signal translating channel comprising, a pair of terminal circuits for said channel, a pair of vacuum-tube repeater devices, means for coupling said devices between said terminal circuits to effect translation of wave signals between said terminal circuits in one direction through one of said devices and in an opposite direction through the other of said devices, each of said devices and its associated coupling means having undesirable capacitive reactance tending to produce undesirable translation of wave signals between said terminal circuits in a direction opposite to its direction ofnormal translation,

means for selectively energizing said repeater devices to effect translation of wave signals in a selected direction between said terminal circuits, and means for reducing the tendency of a selected device undesirably to translate wave signals in the direction opposite to said selected direction translate wave signals in the direction opposite to said selected direction comprising means including the inherent capacitance of the nonselected one of said devices for neutralizing the in herent capacitance of said selected device.

4. A wave-signal translating channel comprising, a pair of terminal circuits for said channel, a pair of vacuum-tube repeater devices, means for coupling said circuits to effect translation of wave signals between said terminal circuits in one direction through one of said devices and in an opposite direction through the other of'said devices, each of said devices and its associated coupling means having undesirable reactance tending to produce undesirable translation of wave signals between said terminal circuits in a direction opposite to its direction of normal translation, means for selectively energizing said repeater devices to effect translation of wave signals in a selected direction between said terminal circuits, and means for reducing thetendency of a selected device undesirably to translate'wave signals in the direction opposite to said selected direction comprising means including undesirable reactance of the nonselected one of said devices and its associated coupling means for translating in said direction opposite to said selected direction wave signals having equal amplitude but opposite phase to the wave signals undesirably translated in said opposite direction by said selected device.

5. A wave-signal translating channel comprising, a pair of terminal circuits for said channel, one of said terminal circuits including a tapped winding, a pair of vacuum-tube repeater devices, means for coupling said ,devices between said terminal circuits to effect translation of wave signals between said terminal circuits in one direction through one of said devices and in an devices between said terminalundesirable reactance tend-,

winding and the undesirable reactance of the nonselected one of said devices and its associated coupling means for neutralizing the undesirable reactance of said selected device and its associated coupling means.

6. A wave-signal translating channel comprising, a pair of terminal circuits for said channel, one of said terminal circuits including a tapped winding providing a winding section on each side of said tap, a pair of vacuum-tube repeaterdevices each including input and output electrodes, means for coupling said devices between said terminal circuits to efi'ect translation of wave signals between said terminal circuits in one direction through one of said devices and in an opposite direction through the other of said devices, each of said devices and its associated coupling means having undesirable reactance tending to produce undesirable translation of wave signals between said terminal circuits in a direction opposite to its direction of normal translation, means for selectively energizing said repeater devices to effect translation of wave signals in a selected direction between said terminal circuits, and means for reducing the-tendency of a selected device undesirably to translate wave signals in the direction opposite to said selected direction comprising means including the undesirable reactance of the nonselected one of said devices and its associated coupling means for neutralizing the undesirable reactance of said selected device and its associated coupling means, said last-named means including a connection of. the output electrodes of one of said devices across one section of said tapped winding and a connection of the input electrodes of the other deviceacross the other section oi said tapped winding.

7. A wave signal translating channel comprising, a pair of terminal circuits for said channel, a pair of vacuum-tube repeater devices each including a cathode circuit, {means for coupling said devices jbetween said terminal circuits to effect translation of wave signals between said termin-a1 circuits in one direction through one of said devices/and in an opposite direction through the other of said devices, each of said devices and its associated coupling .means having undesirable reactance tending to produce undesirable translation of wave signals between said terminal circuits in a direction opposite to its direction of normal translaton, means for selectively energizing the catho, e circuits of said rea pair of vacuum-tube repeater devices'each in cluding input and output electrodes coupling said terminal circuits to effect translation of Wave signals therebetween in one direction'through one of said devices and in an opposite direction through the other of said devices in accordance with selective energization of said repeater devices, a resonant circuit included in said channel and tuned to a selected operating frequency, the input electrodes of one of said devices and the output electrodes of the other of said devices being coupled to said resonant circuit, the impedance values of the input circuit parameters of said one device being so proportioned with relation to the impedance values of the output circuit parameters of said other device in its conductive state that the resonant frequency of said tuned .circuit is substantially constant with selective energization of said devices.

9. A wave-signal translating channel comprising, a pair of terminal circuits for said channel, a pair of vacuum-tube repeater devices each including input and output electrodes coupling said terminal circuits to eifect translation of wave signals therebetweenlin one direction through one of said devices arid in an opposite direction through the other of said devices in accordance with selective energization of said repeater devices, a resonant circuit included in said channel and tuned to a selected operating frequency, the input electrodes of one f said devices and the output electrodes of the .other .of. said devices being coupled to said resonant circuit, a, resistor connected across the input electrodes of said one device, the value of said resistor being so proportioned with relation to the impedance values of the output circuit parameters of said other device in its conductive state that the resonant frequency of said tuned circuit is substantially constant with selective energization of said devices.

10. A wave-signal translating channel comprising, a pair of terminal circuits for said channel, a pair of/vacuum-tube repeater devices each including input and output electrodes coupling said terminal circuits to effect translation of wave signals therebetween fin one direction through i, one of said devices and in an opposite direction peater devices to effect translation of wave signals devices and kits associated \poupling means for through the other of said devices in accordance with selective energization of said repeater devices, a resonant circuit included in said channel. and tuned to a selected operating frequency, the

input electrodes of one of said devices and-the output electrodes of the other of said devices being coupled to said resonant circuit, the output circuit of said other device in its conductive state having a predetermined value of resistance, and a resistor connected across the input electrodes of said one device and having a value of resistance approximately twice thatof the output circuit of said other device to mairitain -the resonant frequency of said tuned circgiit substantially constant with selective energi ation of said devices.

NELSON P. CASE. 

